The present invention relates to optics, generally, and more particularly to a computing system employing optical elements.
Considerable research has been expended on the development of network systems offering greater bandwidth with increased rates of data transmission. Presently, optical network systems operating with greater than eighty (80) wavelength channels and transmission speeds well over ten (10) gigabits per second are commercially available. A laboratory experiment, however, has recently demonstrated transmission speeds of one hundred (100) gigabits per second. For more information, see Mikkleson et al., xe2x80x9cUnrepeatered Transmission over 150 km of Nonzero-Dispersion Fiber at 100 Gbit/s with Semiconductor Based Pulse Source, Demultiplexer and Clock Recovery,xe2x80x9d Electronic Letters, Vol. 35, No. 21 (Oct. 1999), hereby incorporated by reference.
With this rise in transmission speeds and bandwidth capacity, there has also been an increasing load on networks. The load on networks is attributable to a growing number of users seeking network access. The load also relates to an expanding number of applications for such user access. These applications include, for example, e-business activity, corporate websites, as well as intranet and internet access.
The growing demand on networks has also raised concerns regarding data security. Data security entails the use of cryptography. Cryptography may be defined as the science of preventing eavesdroppers from understanding the meaning of intercepted information. For more information, see Schneier, Applied Cryptography, Second Edition, Wiley and Sons 1996 (hereinafter xe2x80x9cSchneierxe2x80x9d), and Koopman, Jr., U.S. Pat. No. 5,696,828 (hereinafter xe2x80x9cKoopmanxe2x80x9d), both of which are hereby incorporated by reference. A cryptographically secure one way transmission of a message includes two primary process steps: 1) encrypting the message using a security key to hide the meaning of the message from eavesdroppers; and 2) decrypting the encrypted message using the security key so the intended user may understand the message.
Presently, the encrypting and decrypting steps are performed while the message and the encrypted message are in electrical form. This is particularly time consuming if the original message is a set of optical signals and conversion to an electrical representation is required. For more information, see Rutledge, U.S. Pat. No. 5,864,625, hereby incorporated by reference. It should be noted that for the purposes of the present disclosure, a message in the form of optical or electrical data is a digital signal employing a binary scheme, as is known in the art. See Hill and Richardson, Introduction to Switching Theory and Logical Design, Third Edition, Wiley and Sons 1981, (hereinafter xe2x80x9cHillxe2x80x9d), pp. 1-21, hereby incorporated by reference. In such circumstances, an optical signal is first converted to an electrical representation, and then encrypted using any variety of techniques known in the art. For examples, see Koopman and Schneier. Thereafter, the encrypted electrical representation is transformed back into an optical format by modulating an optical beam using the encrypted electrical representation, and transmitted to the intended user. The intended user reconverts the received optically formatted signal back into an electrical format. In electrical form, the received signal is then decrypted and may be transformed once again into an optical signal for subsequent processing by the user""s network.
Moreover, the computationally intensive process steps of encrypting and decrypting the data are traditionally performed by semiconductor based Boolean logic circuits. As the demands on networks rise along with transmission speeds and bandwidth capacity, the switching and processing limitations of semiconductor devices will eventually create a bottleneck in providing data security. It is conceivable that in the not so distant future, semiconductorsxe2x80x94comparably faster than present day devicesxe2x80x94may bog down prospective optically based networks for a host of reasons, including security issues. This is based on the historical increases in processing power and switching speeds of semiconductors and the rising bandwidth capacity in optical networks.
Investigative efforts therefore have begun to focus on functional alternatives to semiconductors offering switching and processing times more compatible with network transmission speeds. Research has been aimed at utilizing electro-optics and optical devices to perform various computational Functions. For more information, see Avramopolous et al., U.S. Pat. No. 5,208,705, which is hereby incorporated by reference. These computational functions being explored include combinatorial Boolean logic operations necessary for encrypting and decrypting the data. Boolean logic operations include, but are not limited to, AND, OR, NOT, NAND, NOR, eXclusive-OR (XOR), as well as eXclusive-NOR (X-NOR) functions. See Hill, pp. 22-137, hereby incorporated by reference.
Optical devices for performing logic operations are known. For more information, see Islam, U.S. Pat. No. 4,932,739, and Hansen, U.S. Pat. No. 5,353,114, both of which are commonly assigned with the present invention, as well as Riseberg et al., U.S. Pat. No. 3,984,785 and Jensen, U.S. Pat. No. 4,632,518, all of which are hereby incorporated by reference. However, improvements to optical devices for performing logic operations are still needed.
As such, a demand exists for an optical device to perform computational functions, such as, combinatorial Boolean logic operations, for example. There also exists a demand for an optical device for encrypting and decrypting data.
An optical device for performing at least one computational function is disclosed. In a first embodiment of the present invention, an optical logic device is described which receives typically a first and a second optical input signal. An optical output signal is generated by the device in response to the Boolean operation performed on the optical input signals. The optical logic device may execute various Boolean operations, including AND, OR, and XOR, as well as NOT, NAND, NOR and X-NOR functions. The optical logic device realizes these and other features by including a pair of waveguides and a phase delay element for creating interference.
In one embodiment, the optical logic device incorporates an interferometer, such as a Mach-Zehnder interferometer (xe2x80x9cMZIxe2x80x9d) or Michelson interferometer (xe2x80x9cMIxe2x80x9d). The interferometric device consists of a three port configuration for receiving at least a first and a second input, and for generating an output. The interferometer has at least a first and a second waveguide for respectively receiving the first and second optical input signals. The first and a second waveguide adjoin at an output where the optical output signal is generated. Each waveguide has at least one amplifier, such as a semiconductor optical amplifier (xe2x80x9cSOAxe2x80x9d), integrated therein. Advantageously, the amplifier may be monolithically integrated within each respective waveguide on a single substrate. The amplifiers within each waveguide are configured to create a relative phase difference between the waveguides at the output. The selected relative phase difference corresponds with the Boolean operation of the optical logic device.
In one example, the optical logic device has a relative phase difference of one hundred eighty (180xc2x0) degrees to support an XOR Boolean operation. The truth table reflecting the operation of an XOR Boolean operation is shown in FIG. 3(b). If the first and second input optical signals both represent a binary one, the optical logic device creates an output optical signal representative of a binary zero. A binary zero output is generated here because the relative phase initiates destructive interference, as shown in FIG. 1(a). If both input optical signals represent a binary one, one of the input optical signals is phase shifted by 180xc2x0 relative to the other input optical signal. The phase shifted input optical signal is then combined with the other input optical signal at the output to destructively interfere with each other. In so doing, an output optical signal is created representative of a binary zero. If both input optical signals represent a binary zero, no light travels through either waveguide, resulting in an output optical signal representative of a binary zero. However, if only one of input optical signals represents a binary one, and the other input optical signal reflects a binary zero, an output optical signal is created representative of a binary one. In this circumstance, optical power reflective of the binary one propagates through one waveguide, while the other waveguide does not receive optical power. At the output of the interferometer, the optical power representing a binary one is combined with the optical signal reflects a binary zero to derive the output optical signal equivalent to a binary one.
These and other embodiments, advantages and objects will become apparent to skilled artisans from the following detailed description read in conjunction with the appended claims and the drawings attached hereto.